Single-screw compressors have been used in the art as compressors for compressing refrigerant or air. For example, Japanese Published Patent Application No. 2002-202080 discloses a single-screw compressor including a screw rotor and two gate rotors.
The single-screw compressor will be described. The screw rotor is formed generally in a cylindrical shape with a plurality of spiral grooves cut in the outer circumferential portion thereof. Each gate rotor is formed generally in a flat plate shape and arranged beside the screw rotor. The gate rotor is provided with a plurality of rectangular plate-shaped gates arranged in a radial pattern. The gate rotor is installed in such an orientation that the rotation axis thereof is perpendicular to the rotation axis of the screw rotor, with the gates meshed with the spiral grooves of the screw rotor.
In the single-screw compressor, the screw rotor and the gate rotors are accommodated in the casing, and a compression chamber is formed by the spiral grooves of the screw rotor, the gates of the gate rotors, and the inner wall surface of the casing. As the screw rotor is rotated by an electric motor, etc., the gate rotor is rotated by the rotation of the screw rotor. Then, the gates of the gate rotors relatively move from the start end (the suction side end portion) to the terminal end (the discharge side end portion) of a meshing spiral groove, thereby gradually reducing the volume of the closed compression chamber. As a result, the fluid in the compression chamber is compressed.